Useless

Some of the best things are useless. Fiction books are useless. Mondrian is useless. And so it's Abba. 

Decorative art is slightly different. It produces items that could be used. But their intended function is often ignored. 

For instance, I've never put any of these glass objects to use. Yes, the jug could pour drinks, the vases could contain flowers, the pen holder could hold pens. But they don't. 

If I were to use them, they'd be defined by their usefulness.